I'm having this problem as well. It's very annoying. It won't go away unless I quit opera. For now I have to manually open a new window and copy the URL to the new window instead of dragging the tab out.

I'm having this problem as well. It's not a breaking issue, but it's certainly annoying. The top-bar shows Opera so I just open a new window (command + N). It would be nicer to have this issue fixed though.